cDNA Cloning of the Human Polybromo-1 Gene on Chromosome 3p21

The bromodomain is suggested as a chromatin-targeting domain involved in regulation of gene expression and chromatin structure. We here report the cDNA cloning of the human polybromo-1 ( hPB1 ) gene that encodes a 1634-amino acid polypeptide containing six bromodomains. The hPB1 polypeptide shows 91% identity to the previously identified chicken polybromo-1 with conservation of the bromodomains and other characteristic features. Northern blot analysis detected the ubiquitous expression of hPB1 mRNA in a variety of human tissues. Four alternative splicings were found within the hPB1 coding region: three making in-frame deletions and one resulting in a C-terminal truncation. The hPB1 gene is located on chromosome 3p21, where the tumor suppressor genes for breast, lung and kidney cancers have been mapped.